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Mass extinction

The simultaneous loss of a large number of species over a short time period.

The “Big Five” mass extinctions are events in Earth’s history where a significant portion of Earth’s biodiversity was lost in a relatively short period. These mass extinctions have had a profound impact on the evolution of life on our planet. Here are the “Big Five” mass extinctions:

  1. Ordovician-Silurian Extinction (Late Ordovician, about 443 million years ago): This mass extinction event occurred during the transition from the Ordovician to the Silurian period. It is thought to have been triggered by glaciation and the resulting sea-level changes. Many marine species, especially brachiopods, trilobites, and graptolites, were severely affected.
  2. Late Devonian Extinction (Late Devonian, about 359 million years ago): This extinction event is divided into two separate pulses, each affecting different groups of organisms. The causes of this mass extinction are still debated, but factors such as sea-level changes, climate fluctuations, and anoxia (low oxygen levels) in oceans may have played a role.
  3. Permian-Triassic Extinction (End Permian, about 252 million years ago): Also known as the “Great Dying,” this is the most severe mass extinction event in Earth’s history. It led to the loss of around 96% of marine species and a significant decline in terrestrial life. Multiple factors, including massive volcanic activity, carbon dioxide release, and climate change, likely contributed to this catastrophic event. Trilobites were among the casualties of this extinction event.
  4. Triassic-Jurassic Extinction (End Triassic, about 201 million years ago): This event occurred during the transition from the Triassic to the Jurassic period. While not as severe as the Permian-Triassic extinction, it still had a notable impact on marine life, particularly reef-building organisms. Volcanic activity, climate change, and the breakup of the supercontinent Pangaea are proposed triggers. Some scientists believe during this extinction event there was a partial oxygen deficit that killed many terrestrial animals, but that the dinosaurs were able to survive because they were adapted to higher elevations than many of the non-dinosaurian larger animals.
  5. Cretaceous-Paleogene Extinction (End Cretaceous, about 66 million years ago): This is perhaps the most famous mass extinction event due to its association with the extinction of non-avian dinosaurs. The impact of an asteroid or comet (the Chicxulub impactor), along with volcanic activity (especially the Deccan traps) and resulting climate change, is believed to have caused widespread environmental disruptions and the collapse of ecosystems.